Radiation has been employed to obtain images of patients for medical purposes. For example, in a computed tomography (CT) procedure, a diagnostic energy beam is applied from an external source towards the patient from different gantry angles to obtain different respective projection images. The projection images may then be used to reconstruct a volumetric image. The volumetric image may be used to examine tissue for diagnosis purpose and/or for treatment planning purpose.
In some cases, different volumetric images for different respective phases of a physiological cycle are obtained, and the different volumetric images may be displayed in a time or phase sequence to form an animated image, or movie (4D CT). Such a movie allows a physician or a treatment planner to see how different tissues move as the patient experiences physiological movement, thereby allowing treatment planning to incorporate patient movement. Procedures for 4D CT involve obtaining projection image data for different phases of a motion cycle (e.g., respiratory, cardiac), and then using the image data to reconstruct volumetric images for different phases. The resulting images may be displayed in a sequence to form a video.
Currently, the entire image data set for a volumetric image is stored. For the case of a 4D CT image set, the entire image set is also stored. For the case of a sequentially registered 4D CT image set, registration matrices connecting each phase are also stored. Applicant of the subject application determines that individually storing each of the pixel values in a volumetric image, or individually storing each of the pixel values in each of the volumetric images in a movie along with the registration matrices, requires significant storage space. Thus, Applicant determines that a system and method for compressing and decompressing image data would be desirable.